Fast, corrosion resistant joining of sheet steel structure

[CalculatorDave]

Hello all,

My question concerns "design for corrosion resistance" and "design for automation" of the joints of a sheet steel structure. The structure operates outdoors, with an expected service life of 20 years.

Our sheet metal structure is made from pre-galvanized sheet steel. Our current joining method is clinching. Clinching´s advantages to us are (1)doesn´t harm the sheet steel´s galvanizing layer and (2) doesn´t require precise hole alignment (no holes at all). Clinching´s disadvantages to us are (1) relatively slow cycle time (1 second) and (2) not the ideal method for our material thickness (our material is relatively thick for clinching).

Spot welding seems to be the fastest method for sheet metal joining. However, the weld heat will vaporize the zinc layer in the weld region. Re-coating with a cold galvanizing coating is not an option. We COULD select a non-galvanized material that is inherently corrosion resistant - I´ve already thought of aluminum (not stiff enough) and stainless steel (too expensive).

Self-piercing rivets are too slow. Blind rivets require precise hole alignment.

We´ve already reduced the number of joints in the structure, in order to reduce total joining time.

Do you see any way that I can make spot-welding work?

Thank you,

SD

 

[mloew]

What about Hot-dip galvanizing after fabrication? As for stainless steel, are you considering the total costs, or just the material costs. For many designs I have seen stainless steel can be economically substituted for conventional steel and the corrosion coating. This is especially true when the designs are strength limited and high-strength stainless can be used.

Best regards,

Matthew Ian Loew


Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[aamoroso]

When we spotweld galvanized (daily at our shop) we vaporize the the zinc between the sheets and allow it time to escape then continue to spot weld the sheets. All of our product then goes through a powder coat system which applies zinc phosphate to the surface. Unpainted product gets a shot of Zinc Coat spray. Sounds like this may not be acceptable for your application? We build outdoor enclosures for Cable and Tele industry as well as enclosures for Air conditioning equipment.

Fill what's empty. Empty what's full. And scratch where it itches.

 

[mloew]

One more thing, what about self-piercing rivits?

Best regards,

Matthew Ian Loew


Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[griffengm]

Solar Dave,
We handle spotwelded galvanized by two methods. One was to wash the part, prime the HAZ with a zinc paint and then paint with a baked enamel. The second was to clean and paint with an epoxy paint. Both gave respectable results. I used the past tense because we converted the parts involved to plastic about four years ago.
We also had some parts that were arc welded that we handled much the same way but which we eventually converted to plastic as well.
We had also looked at blind rivets but felt that the process was slow. We use some for dissimilar materials or where a screw might be objectionable.
We looked at self piercing rivets but like yourselves felt that they were slow although we liked the flush surface and color match capabilities.
Just another POV.

Griffy